In article ,
Owen Duffy wrote:

A well executed ground plane antenna is an antenna that a person with
little knowledge and experience can implement with a high level of
confidence that it is reasonably efficient and effective.

That would certainly be another workable alternative for this
situation. An SO-239, a few feet of 10-gauge solid wire, and a bit of
soldering, and you end up with a ground-plane antenna with a hanging
loop at the top, two or four ground radials drooping at around a
45-degree angle, and a near-ideal match to 50-ohm coax. Cheap and
quick to make. Stick a ferrite or two on the feedline just below it,
and feedline radiation shouldn't be a problem. If I recall correctly,
this very design appeared in the "quick tips" freebie blurb I got from
the ARRL after I first got my ticket.

It seems to me that the preferred method from purely an electrical point
of view is none of those three. If you establish the tapping point,
drill a hole in either tube at that point, and another at the bottom of
the U, then pass the coax up through the bottom hole inside the tube
(bonding the shield to that point), exit through the other hole bonding
the coax shield to the tube and connecting the inner conductor to the
opposite side, you have built an integral balun which helps to reduce
common mode current. A further ferrite balun below the tube somewhat
using say #61 would give improved suppression at 144MHz.

I used that very design to build a two-arm "Copper Cactus", with
separate stubs and feedlines for 2 meters and 440. It seemed to work
well (although I never actuually measured the feedline currents).

One gotcha to this approach - you have to be *very* careful to
waterproof the point where the coax exits from the upper hole and has
its shield bonded to the pipe! If you don't get a thoroughly
waterproof coating of silicone sealant (or something similar) here,
the exposed braid will wick up water during every rainstorm which
comes along, and your coax will turn into a hose.

The SWR on mine went sky-high after a winter up in the California
rains. When I disconnected the N connectors down at the base of the
antenna, I found them full of water and algae(!) and had a devil of a
time getting things dried out again.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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